Practical Organic Chemistry

124 PRACTICAL ORGANIC CHEMISTRY

PREPARATION 36.
Pyruvic Acid, CH3.CO.CO.OH.
Doebner, Annalcn, 1887-, 242, 268.
200 grms. potassium hydrogen sulphate.
100 „ tartaric acid.
The potassium hydrogen sulphate and tartaric acid must toe
finely powdered and intimately mixed. The mixture is distilled
in a round flask (i litre), attached to a moderately long condenser
tube, from a paraffin bath heated to 220*.* The mass at first
froths up, and it is necessary to interrupt the heating when tlie
flask is not more than half full of froth, as otherwise it mny
boil over. When the temperature of the bath has fallen to
about I2OC, the heating may be recommenced. The distillation
is carried on until no more liquid distils. The distillate, whicli
consists of water and pyruvic acid, and has a yellow colour, is
fractionated in vacuo. It is collected at 68—70° at a pressure
of 20 mm., and is quite colourless. Yield 15—20 grams. It
may be fractionated at the ordinary pressure, but is difficult to
obtain colourless in this way.
CO.OH.CHOH.CHOH.COOH = CH3.CO.COOH + CO2 + H2O
Properties.—Colourless liquid; b. p. 165° at atmospheric:
pressure ; m. p. 10—11°; polymerises on keeping.
Reaction.—Dissolve a drop of phenylhydrazine in two drops
of glacial acetic acid, dilute with about i c.c. of water, and acid
a drop of pyruvic acid. A yellow crystalline precipitate of tlie
phenylhydrazone, CH3.C:(N.NH.C0H6).CO.OH, is formed.
CH2.COOH
Citric Acid, C(OH).COOH + H2O *•
CH2.COOH
Scheele (1784).
Citric acid occurs in the free state, as well as in the form, of
the calcium and potassium salts, associated with malic and ta.r-